Electro-ionic printing

ABSTRACT

A method of forming electrostatic images on a dielectric surface by controlling the relative ion concentration in a gas stream moving through a channel and directed upon said dielectric surface. Application of an electric field across the channel enables the stream to vary in ion concentration so as to cause the formation of a desired linear charge configuration on the dielectric. Selective application of electric fields to an array of channels causes formation of desired image charge configurations on the dielectric surface.

[ 1 Apr. 3, 1973 Mutschler et I ELECTRO-IONIC PRENTING 3,495,269 2/1970.346/74 EB 3,117,022 l/l964 Bronson et al............... ....346/74 EB[75] lnventor: Robert E. McCurry, Vestal, N.Y.

[73] Assignee: International Business Machines Primary Examiner-BernardKonick Assistant Examiner-Jay P. Lucas Attorney-Andrew Taras et al.

Corporation, Armonk, N.Y.

June 16, 1971 [22] Filed:

[57] ABSTRACT A method of forming electrostatic images on a dielec- 21Appl. N0.: 153,718

tric surface by controlling the relative ion concentration in a gasstream moving through a channel and directed upon said dielectricsurface. Application of an electric field across the channel enables thestream to vary in ion concentration so as to cause the forma- 250/49.5GC, 41.9 SE

tion of a desired linear charge configuration on the dielectric.Selective application of electric fields to-an References Cited UNITEDSTATES PATENTS array of channels causes formation of desired imagecharge configurations on the dielectric surface.

....346/75 4 Claims, 10 Drawing Figures Morgan...... Rourke ION HEADASSEMBLY DIELECTRIC MEDIUM LINE OF DOT IMAGES PATENTEDAPR3 1975 SHEET 1UF 3 FIG. 1

4 ION HEAD ASSEMBLY DIELECTRIC MEDIUM CHARACTER PULSING MEANS POWERSUPPLY FIG. 2

INVENTOR ROBERT E. McCURRY AGENT PATEIHEDAPM 1975 7 5,951

SHEET 2 OF 3 ELECTRICAL BIAS MEANS MEANS 0PM) F decided advantage overthe prior art printing techniques by virtue of the factthat:

rather than by an accelerating electric field.

it does not have to cause breakdown; hence the control voltage and powerare reduced by orders of magnitude compared with other techniques.

ELECTRO-IONIC PRINTING BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates broadly to the control of the ionconcentration in a gas stream, and more particularly to the formation ofan image on a dielectric surface by directing thereon a controlledconcentration of ions borne by the gas stream.

2. Description of the Prior Art The prior art is replete with a widevariety of means The most pertinent art is found in US. Pat. No.

3,495,269 issued to Mutschler et al. in which latent image formation isproduced as a result of an ion charge produced in the air gap betweenthe head and the image receiving surface. This charge is the result ofelectrical breakdown in the air gap caused by de-excitation ofMetastable Helium atoms, the latter being generated by the applicationof high electric fields to helium atoms.

SUMMARY OF THE INVENTION The present invention, on the other hand,employs a relatively simple means for controlling the ion concentrationin a moving gas stream directed upon a dielectric surface to cause theformation of a desired latent image.

Accordingly, it is the principal object of the invention to provide aunique method for controlling ion concentration in a moving gas stream.

Another object is to provide a relatively simple and inexpensive methodfor forming latent images on a dielectric surface.

Yet another object is to provide a relatively simple and inexpensivemethod for forming latent images on an image receiving surface bycontrolling ion concentration in a moving gas stream directed on saidsurface.

Still another object is to provide electrostatic images of a highquality and resolution on a dielectric surface.

Aside from these various objects, the invention has a Any gas can beused in which stable corona can be generated. It is not limited to He orinert gases.

Ions are transported primarily by the gas stream hence no erosion orother deterioration effects.

Electrical control has only to move ions across a gap,

Metastable atoms are not required.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows an ion head assemblygenerating a plurality of individual ion streams.

FIG. 2 is a schematic arrangement of the invention showing 3 channels ofthe head assembly interconnected between a DC power supply and acharacter pulsing means.

FIG. 3 is a schematic arrangement of a printer utilizing the headassembly of FIG. 1.

FIGS. 40, 4b, and 40 show schematically the 7 channels of a write headand the pulse patterns for forming images of the alphabetic characters Eand H, respectively.

FIGS. 5a, 5b, and 5c show diagramatically how ion concentration iscontrolled in a channel of the ion head.

FIG. 6 shows ion current pulse behavior according theory.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of controlling astream of gas borne ions may be explained in connection with FIG. 1herein is shown an ion generating chamber 1, similar to the one shownand described in a copending application, Ser. No. 69,647, filed Sept.4, 1970, titled Method and Apparatus for Generating ElectrostaticImages. A gas,

- for example air under pressure is admitted into the ion chamber by wayof an inlet 2 and the ions are generated in the manner described in saidcopending application. The gas exiting from ports 3 is laden with a veryhigh concentration of ions. Each port 3 communicates with an individualchannel of which there are 7 such channels namely 4a1-4a7 constituting ahead assembly 4. Each channel is constituted of electrical conductingtop and bottom wall membersSa, 5b and insulating side walls 6. The headassembly 4 is held together and at tached to the ion chamber by anysuitable means not shown. It is thus seen that the head assembly 4provides a plurality of longitudinal channels insulated from each otherto provide a plurality of individual ion streams, each of high ionconcentration. The cross-section of each channel may be any suitableconfiguration, for example, square, rectangular, or any other desiredcrosssection. Attached to the top and bottom walls Sal-507, 5bl-5b7 areelectrical lines 15a-15g, l6a-16g. Lines 16a-16 are connected in commonto a DC power supply, while the lines ISa-lSg are individuallycontrolled by differentially timed pulses issued by a character pulsingmeans, cpm.

As the gas streams pass through their respective channels ionconcentration decreases as a result of recombination and neutralizationat the channel walls. The ion loss through a conductive wall may besubstantially increased by superimposing an electrical field acrossopposing channel walls, for example, the top and bottom walls.Application of a sufficiently large electrical field will removesubstantially percent of the ion concentration in the gas stream.Conversely, the

The electrical field is induced by application of an electricalpotential through the lines 150-153 connected to the opposing walls ofthe channels shown in the drawing of FIG. 1. The write state of achannel is attained when a low or zero transverse electrical field isapplied, and the off state is attained with the application of a greaterbiasing electrical field to remove more ions from the gas stream. In thecase of a printing'application, the variation of the electricalpotentials to produce character printing is controlled by the characterpulsing means, cpm.

The application of desired electrical fields to a write head 4 isschematically illustrated in FIG. 2 In this schematic arrangement, thewrite head 4' partially shown with 3 capacitors, representing 3 channelsshown in FIG. 1. The plates Sal, 5bl, of the capacitors, correspond tothe top and bottom channel walls respectively. Each capacitor is seenconnected'between the character pulsing means (cpm) by way of linesa-15g and the DC power supply, the latter being adjusted to a desiredpotential V to obtain the desired ion output. The character pulsingmeans, cpm, supplies pulses of appropriate polarity and magnitudesubstantially equal to the potential V of the power supply. During theinterval of time that a write operation is desired the field across thecapacitors (the channel) is reduced to enable the ion concentration toattain its maximum concentration and be directed against an imagereceiving surface for the formation of a desired image configuration.

An application of this type of ionic control is seen in FIG. 3 whichshows schematically a printer arrangement for forming a latentelectrostatic image upon a dielectric medium moving from right to leftunderneath a precharging unit 21 that precharges the medium 20 with adesired potential with polarity op posite the ion polarity. Theprecharged dielectric medium moves underneath a write head 4" similar tothat described above. The write head communicates with ion generator 1By controlling the individual channels of the write head with suitablevoltage pulses, a latent image of alphabetical characters is formed uponthe 'precharged dielectric surface of medium 20. The medium 20 with itslatent image passes through a developer 22 and thereafter through afixer 23, both of which are well known in the art. After passing throughthe fixer the latent image is developed and fixed to provide a visibleimage comprised of two alphabetic characters E and H. The characterpulse means as mentioned herein write head channels. The formation ofalphabetical characters by means of printer arrangement of FIG. 3 may bedescribed with reference to FIG. 4a, 4b, and 4c.

The schematic arrangement of FIG. 4a shows a line arrangement of 7capacitors representing 7 channels of the write head. The left sides,5al-5a7 of the capacitors are connected to 15 volt DC supply whereas theright sides, 5b1-5b7 of the capacitors are connected to the characterpulsing means, cpm, not shown, that selectively pulses the right sidesof these capacitors to cause formation of the desired latent image onthe dielectric medium 20. From an inspection of FIG. 4b it may beappreciated that in the formation of the image of the character E thevertical segment of the character E is formed during the intervalVTduring which there is no electrical field present across the channels ofthe write head and during this intervalVT the character pulsing meanssupplies l5v pulse potential to the appropriate channel walls of allchannels. From a further inspection of FIG. 4b it is seen that the upperand lower horizontal lines, as well as the central horizontal line, ofthe character E are formed during the application of l5v potentials tothe channel walls represented respectively by capacitors 4al, 4a4, and4a7 shown in FIG. 4a for approximately 5 time intervals. At the end ofthe first time intervalVT the character pulsing means applies zerovoltage to channel walls represented by 5b2, 5b3, 5b5, and 5b6. Thesefour walls are maintained at zero potential for the duration of thecharacter formation. The l5v potential on wall SM is maintained on for 4time intervals. It is understood that the latent image is being formedon the dielectric medium as the latter moves from right to left underthe respective channels of the write head.

From an inspection of FIG. 4c it can be appreciated that the pattern ofpulses'applied to the respective channels 4a1 through 4a7 is consistentfor the formation of the alphabetical character H. 5

Although the precise mechanism may not be fully known, nevertheless adiscussion of the theoretical aspects and behavior of ionic action canbe offered to provide a reasonable explanation of what occurs in thecontrol of ion concentration in a moving gas stream passing through achannel head-without in any way limiting or restricting the scope of theinvention. In this vein the following theoretical discussion issubmitted as a plausible explanation of ionic action that may occur inthe formation of a desired image utilized, for example, in the printingof characters using a head configured according to certain desiredparameters.

Suppose ions of concentration n are distributed uniformly across theentrance to a rectangular crosssection channel head in a uniformelectric field and that the velocity of gas through the channel head isV,,.

The time required for a molecule or ion to pass through the channel headof Length, L, is T,=L/ V,,.

The time for an ion of mobility p. to drift across the channel headwidth is T =W/V =W /;LV I (2) Neglecting neutralization timesubstantially all ions ing the bias potential V to make ol V S (4) Whenthis Condition is not satisfied, ions that are transmitted arenonuniforrnly distributed, i.e., substantially all ions will be removedfrom the cross-sectional area (a X X) where a is the electrode width andSeeFIGS. 5a-5c.

Under these conditions, the transmitted ion current is q W-X) 6) Where qis the charge per ion.

The ion current density changes from 0 to nq V, at a distance X from thecollector electrode. From this point of view the difference between ONand OFF conditions is the cross-sectional area through which ions aretransmitted.

If .we now consider the charge density which can be delivered to anddeposited on a dielectric (relative velocity, V,,.) moving parallel tothe direction in which W and X are measured, ignoring spreading causedby space charge and viscosity effects, then charge density deposited isAs in other electrostatic image formation techniques, the voltagecontrast produced is proportional to the difference in surface chargedensity. The proportionality constant being the reciprocal ofcapacitance per unit area. Thus in the case above the change in surfacepotential produced on a dielectric sheet of thickness d, and dielectricconstant K is V.= o Q. (8)

And the width of a written-line would be a and its length V, X T,,,where T,, is the on time.

Thus far it has been assumed that transients, i.e., turn on and turn offtimes are not limiting factors, hence surface charge density will changeas indicated by (7) rather than by some smaller amount. It is, however,of interest to consider the on-off transient behavior expected from thistype of write-head.

In the simple theory considered here, the ion trajectories are juststraight lines. If we consider turmon time first, (in response to a stepinput), we see that the total tum-on transient time is equal to thetransmission time, T given by (1).

A part of this time will, however, be a simple delay if T Tthat delaytime is just T ==T T After 713 has elapsed, the ion current riseslinearly to its on-value, reaching it at time T Notice that if T 2 Tthen T =0, and the ion current begins to rise immediately. The situationis illustrated in FIG. 6.

If we now consider tum-off time, we note first that there is nocomparable delay time, i.e., the ion current immediately begins todecrease. However, transient time in this case is given completely by Tup to a maximum of T I One can therefore expect on the basis of thesetransient time considerations that line length for as well as of pulselength.

Thus far we have neglected the uniformity of ion distribution emergingfrom the head cross-section and considered only total current. Since thetransients considered above are, in the simple theory, just associatedwith a one-dimensional change of the area of the head through which ionsare transmitted, and since with present geometry the changing onedimension is parallel to the direction of V one expects that writtenlines may show a directional effect associated with dielectric motion.Hence, the leading and trailing edges of a line may differ and theleading edge should be sharper than the trailing edge for dielectricmotion from the ion collector channel wall to the opposite wall and alsosharper for this motion from rather than toward the collector.

Typical bias voltage values that work fairly well are 15 volts and it isestimated that ion mobility is 1-2 cm /v-sec. Hence, T -5 to 10 X 10'sec. This value of T represents a factor of 10 smaller than one wouldexpect.

The value of T is expected to be much more reliable, and one may take Tas best estimate of the transient on-time some part of which may be acomplete delay. An important point here is that this time isapproximately equal to the transient time (i.e., a point on thedielectric sheet will traverse the slot width in approximately the sametime as the transit time). This should lead to a much sharper edge inone direction than in the other, i.e., gradient of charge density ismuch larger on one edge than on the other.

It may be worthwhile at this point to get a more quantitative idea ofthe magnitude of this effect. Considering that the off ion profile in ahead is simply a wedge, and. that during turn-on" and tum-off transientsthe wedge moves down the channel toward the paper or back up toward theion generator respectively, one can calculate the sharpness of theedges, i.e., the distance over which charge density varies.

The result is es p/ 2) S W for'V and V in the same direction, the orexponent is chosen so that and W W+T V W (10 for V and V in oppositedirections.

In these expressions, T is the surface transport time across the slotwidth, i.e., T,,=W/ V,,

V is the velocity of the ion profile across the channel width, i.e., VW/T velocity in the forward direction is just V,,, the gas flowvelocity.

From expressions 9 and 10 the charge density gradient depends on thedirection of relative motion of the dielectric surface, and the polarityof the head that determines which electrode acts as ion collector. Inparticular, from (9), a leading or trailing edge can be made ideallysharp for T,,=T while the other cannot, i.e., the gradient of chargedensity will be non-zero over a distance greater than the slot width.The result is a directional nature which can be minimized by minimizingT i.e., this procedure makes W W.

While the invention has been particularly shown and streams to produceionically modulated streams; described with reference to preferredembodiments and thereof, it will be understood by those skilled in theart directing said modulated streams upon said dielectric that theforegoing and other changes in form and surface to form said latentimage, the potential details may be made therein without departing fromthe across said field being substantially less than the spirit and scopeof the invention. breakdown potential of said gas.

We claimi 2. The method of claim 1 in which said individual ion 1. Ameth d f f r in a lat nt l t t i image streams are configured with adesired cross section. on a dielectric surface comprising: 3. The methodof claim 1 in which said electric fields generating a high concentrationof ions in a pre 10 are varied so to provide variations in the intensityof surized gas in a chamber; 531d lmagesforming a plurality ofindividual ion streams from the method P clam 1 l" which 3 dlelectl'lcionized pressurized gas chamber; face is moved during formation of theimage. selectively applying a transverse electric field to said

1. A method of forming a latent electrostatic image on a dielectricsurface comprising: generating a high concentration of ions in apressurized gas in a chamber; forming a plurality of individual ionstreams from the ionized pressurized gas chamber; selectively applying atransverse electric field to said streams to produce ionically modulatedstreams; and directing said modulated streams upon said dielectricsurface to form said latent image, the potential across said field beingsubstantially less than the breakdown potential of said gas.
 2. Themethod of claim 1 in which said individual ion streams are configuredwith a desired cross section.
 3. The method of claim 1 in which saidelectric fields are varied so to provide variations in the intensity ofsaid images.
 4. The method of claim 1 in which said dielectric surfaceis moved during formation of the image.